1. Field of the Invention
The present invention relates to an image forming apparatus that functions to form images on both sides of a sheet.
2. Description of the Related Art
Hitherto, in some image forming apparatuses such as copying machines and page printers, after reversing a sheet having an image formed on one (front) side, the sheet is transported again to an image forming section to form an image on the other (rear) side of the sheet. Such an image forming apparatus includes a duplex (double-sided) feed mechanism for reversing a sheet having an image formed on one side, and then transporting the sheet again to the image forming section.
There is also known an image forming apparatus provided with a mechanism for reversing each sheet from a face-up to a face-down state before ejection so that sheets having images formed thereon are ejected in proper page order.
Then, a demand for increasing the efficiency in operation of those duplex feed mechanism and reversing mechanisms has arisen.
For example, a duplex feed mechanism disclosed in Japanese Patent Laid-Open No. 58-182655 includes a duplex copying aid means that comprises a sheet ejection section, a switching gate, a switchback section, a return section, and a reversing section. When copying an image on the rear side of a sheet on the front side of which an image has been copied, the duplex copying aid means increases a copy return speed so that the sheet having finished copying of an image on the front side more quickly reaches a predetermined return position from which copying of an image on the rear side can start. As a result, efficiency of duplex copying can be increased.
In the conventional image forming apparatus including the duplex feed mechanism to increase the speed in transporting a sheet, on one side of which an image has been printed, to a reversing unit as disclosed in Japanese Patent Laid-Open No. 58-182655, a great improvement in processing speed cannot be expected even though a slight increase in speed of the duplex image formation is expected.
Also, in an apparatus provided with a plurality of sheet reversing routes as disclosed in Japanese Patent Laid-Open No. 6-35265, the overall size of the apparatus is enlarged, the cost is increased, and the apparatus is not satisfactorily convenient for users.
Meanwhile, speedups in operation of image forming apparatuses have increased the output volume in recent years. Correspondingly, a problem has occurred with an increase of the time during which the image forming apparatus cannot be temporarily used, i.e., the so-called xe2x80x9cdowntimexe2x80x9d, and how to reduce the downtime has become a very important issue to be overcome. The downtime is increased because of a part failure, a sheet jam, and other troubles.
In view of the state of the art set forth above, it is an object of the present invention to provide an image forming apparatus capable of forming images on both sides of a sheet at high speed, and with reduced downtime.
To achieve the above object, the present invention provides an image forming apparatus comprising an image forming section; a plurality of reversing units each for reversing a sheet having an image formed thereon by the image forming section; and a control unit for controlling the plurality of reversing units so that when one of the plurality of reversing units is unusable, a sheet feed operation continues using reversing units which are usable.
Also, the present invention provides an image forming apparatus comprising a reversing feed path for reversing a sheet; a re-feed path for re-feeding the sheet having been reversed in the reversing feed path to the image forming section; a reversing inlet feed path for transporting, to the reversing feed path, a sheet having an image formed on one side by the image forming section; a plurality of reversing outlet feed paths branched from the reversing feed path at plural points and for transporting, to the re-feed path, the sheets having been transported to the reversing feed path; and a control unit for controlling the plurality of reversing outlet feed paths so that when one of the plurality of reversing outlet feed paths is unusable, a sheet feed operation continues by using reversing outlet feed paths which are usable.
Further, the present invention provides an image forming apparatus comprising a reversing feed path for reversing a sheet; a re-feed path for re-feeding the sheet having been reversed in the reversing feed path to an image forming section; a plurality of reversing inlet feed paths joining with the reversing feed path at plural points and transporting, to the reversing feed path, sheets each having an image formed on one side by the image forming section; a plurality of reversing outlet feed paths branched from the reversing feed path at plural points and for transporting, to the re-feed path, the sheets having been transported to the reversing feed path; and a control unit for controlling the plurality of reversing inlet feed paths so that when one of the plurality of reversing inlet feed paths is unusable, a sheet feed operation continues by using reversing inlet feed paths which are usable.
Still further, the present invention provides an image forming apparatus comprising a main feed unit for feeding a sheet having an image formed thereon by an image forming section; a first sheet switchback transport unit and a second sheet switchback transport unit arranged side by side, for transporting the sheet fed from the main feed unit to a downstream side when rotated forward, and then for transporting the sheet backward to an upstream side when rotated backward; a sheet switchback transport path selecting unit for selectively advancing the sheet fed from the main feed unit to the first sheet switchback transport unit and the second sheet switchback transport unit; a failure detecting unit for detecting a failure in operation of at least one of the first sheet switchback transport unit and the second sheet switchback transport unit; and a control unit for controlling the first sheet switchback transport means and the second sheet switchback transport means so that when information indicating a failure in operation of one of the first sheet switchback transport unit and the second sheet switchback transport unit is recognized based on information from the failure detecting unit, operation of the non-failed sheet switchback transport unit continues.